Juvenile dermatomyositis (JDMS) is a systemic vasculitic inflammatory disease. There is an increased frequency of both neutralizing and complement fixing antibody to an enterovirus, Coxsackievirus B (CVB), in newly diagnosed JDMS. This laboratory has recently presented data showing that most JDMS children have a restricted HLA repertoire: B8/DR3 (C4A deletion as part of linkage disequilibrium) with an increased expression of DQA1 4.0. We now hypothesize that JDMS patients have a limited expression of the TCR+ Vbeta variable regions which recognize CVB antigenic epitopes in the context of the disease associated DQ restriction element on the antigen presenting cell (APC). Specific aim #1-a will characterize the TCR composition of the T cell infiltrate in a least 20 JDMS muscle biopsies compared with peripheral blood mononuclear cells (PBM) from 30 age-grouped normal children and 10 adults, using monoclonal antibodies directed against a) T cell antigens CD4/8 and CD3, and b) framework determinants of the TCR receptor alpha/beta and gamma/delta chains to determine if there is selective enrichment of TCR+ alpha/beta+ T cells in diseased muscle. Specific aim #1-b will prospectively compare, in at least 5 muscle/peripheral blood pairs from untreated children with JDMS, the relative proportions of TCR+ cells expressing alpha/beta as opposed to gamma/delta antigens, to determine if there is selective TCR+ alpha/beta+ T cell enrichment in inflamed muscle during the initial stages of the disease. Specific aim #1-c will determine, using quantitative PCR, if there is specific expression of one or more regions of the Vbeta gene as compared with the Valpha gene in JDMS muscle infiltrate. Specific Aim #2 will focus on the role of both MHC and TCR in CVB antigen recognition, using CVB antigen specific T cell clones developed from JDMS patients compared with normal DR3+ and DR3- donors to determine a) specific TRC variable gene utilization in CVB recognition and response as determined by PCR and b) the role of the MHC in the APCs using 1) Class II specific blocking antibody and autologous APCs and 2) DR3+, DQA1+ Class II lymphoblastoid cell lines and their controls as APCs. Comparison of TCR populations will use chi square analysis; T cell clone responses will be compared using group means and the Student's paired t-test. If there is limited TCR gene expression in both the JDMS muscle and antigen reactive T cell clones, alternative modes of therapy might be considered.